Project B8 (finished)

Background and Motivation

Driving a fuel cell system in aircraft operation is a challenging task. Air feed fuel cells meet variable environmental pressure levels in regular aircraft operation. The variation of the system pressure results in changes of fuel cell performance. The project aims to measure the performance and efficiency of a polymer electrolyte membrane fuel cell system subject to ambient and low pressure conditions. The very first low test pressure test facility was assembled by the German Aerospace Center, Institute of Engineering Thermodynamics. The fuel cell system is subject to different operation parameters (pressure, cooling temperature, stochiometry and load requirement).

Aims and Objectives

It is virtually impossible to explore all the different combinations of operating parameters in an experimental set-up. Therefore, an experimental set-up based on the concept of Design of Experiments was computed before the measurements were started. This methodology allows to use much fewer but carefully chosen experimental runs. Stated differently, the 'design-space' is allowed to be as sparse as possible.

Mathematically, the concept may be based (other criteria are possible) on maximizing the differential Shannon estimates of the parameter estimates. Loosely speakings, by maximizing the determinant of the inverse of the variance matrix, it is attempted to maximize the 'available information'. Maximizing the determinant of a matrix requires the iterative solution of a non-linear optimization problem.

However, this work must be repeated regularly: it turned out during experimental runs that there are many non-admissible operation areas especially at low pressure operation. As a result, desired points in design-space cannot be reached since they might damage the fuel cell system. As this only shows up while the experiments are running the points in design-space must be redistributed in real-time.